Nipple-electrode assembly and joint

ABSTRACT

The invention relates to nipple-electrode pre-assemblies and joints, such as those used on electric furnaces, and to a method of distributing thread clearance throughout the preassembly and/or joint. This method includes: the providing of at least one lengthwise hole between each end of the nipple, said hole being substantially axial or parallel to the axis and internally threaded for at least a portion of its length; the prepositioning of the nipple in the socket of the electrode section into which the nipple is threaded so as to provide a clearance between the non-load bearing flanks of the nipple threads and said threaded electrode socket; and the insertion within one end of the lengthwise hole and the space between the base of the nipple and the bottom of the socket of the electrode section of a mechanical adjusting member having external threads which correspond to the internal threads of the lengthwise hole, which member by adjustment with a suitable tool inserted into the hole of the projecting end of the nipple and by turning within the threaded lengthwise hole, thereby causes or is capable of causing relative axial movement of the nipple with respect to the electrode section so as to bring or keep the load bearing flanks of the nipple threads and the electrode socket section threads into contact securing the nipple in this position. This thus provides and/or maintains the aforedescribed pre-positioning and thread clearance and thereby also provides room for any excessive diametrical expansion of the nipple over that of the electrode socket when the assembly is heated during service.

United States Patent Whitwell NIPPLE-ELECTRODE ASSEMBLY AND JOINT [75]Inventor: James H. Whitwell, Lockport, NY.

[73] Assignee: Great Lakes Carbon Corporation, New York, NY.

22 Filed: Aug. 30, 1971 21 Appl.No.: 176,013

Primary Examiner-David .l. Williamowsky Assistant Examiner-Wayne L.Shedd Attorney--Wallace F. Neyerlin [57] ABSTRACT The invention relatesto nipple-electrode preassemblies and joints, such as those used onelectric [451 Nov. 13, 1973 furnaces, and to a method of distributingthread clearance throughout the preassembly and/or joint. This methodincludes: the providing of at least one lengthwise hole between each endof the nipple, said hole being substantially axial or parallel to theaxis and internally threaded for at least a portion of its length; thepre-positioning of the nipple in the socket'of the electrode sectioninto which the nipple is threaded so as to provide a clearance betweenthe non-load bearing flanks of the nipple threads and said threadedelectrode socket; and the insertion within one end of the lengthwisehole and the space between the base of the nipple and the bottom of thesocket of the electrode section of a mechanical adjusting member havingexternal threads which correspond to the internal threads of thelengthwise hole, which member by adjustment with a suitable toolinserted into the hole of the projecting end of the nipple and byturning within the threaded lengthwise hole, thereby causes or iscapable of causing relative axial movement of the nipple with respect tothe electrode section so as to bring or keep the load bearing flanks ofthe nipple threads and the electrode socket section threads into contactsecuring the nipple in this position. This thus provides and/ormaintains the aforedescribed pre-positioning and thread clearance andthereby also provides room for any excessive diametrical expansion ofthe nipple over that of the electrode socket when the assembly is heatedduring service.

3 Claims, 7 Drawing Figures PATENTEurmv is191s 3371.886 sum 1 BF 2INVENTOR. JAMES H. WHITWELL PATENTEIlnuv13 I975 3.771.886 em 2 BF 2 X 7INVENTOR. 50. JAMES H. WHITWELL NIPPLE-ELECTRODE ASSEMBLY AND. JOINTBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to the field of graphite or other carbon electrodes for electricfurnaces and like equipment, wherein the electrodes are consumed in useand must be continually fed into the furnace or other equipment wherethey are used.

It particularly relates to electrode joints that comprise adouble-frusto-conical threaded connecting nipple of electrode materialwhose two frusto-conically tapering portions are in threaded engagementwith respective frusto-conical cup-shaped socket recesses in the buttfaces of the coaxially aligned electrodes and'to the manner in whichsuch a joint is assembled. However, the threaded nipples and theircorresponding sockets or bore holes in the electrode sections may alsohave threaded sides which are parallel to the nipple axis. Such jointsserve to add a new electrode to the end of a nearly consumed electrodeto permit a continuous furnace operation by replenishing the electrodematerial in accordance with the rate-of consumption.

In making such joints, one end of the nipple is screwed into place in acorresponding bore or socket of one of the electrodes to the approximatemiddle of the nipple and then the other electrode section is threaded tothe otherend of the nipple until the faces of the electrode sections arein contact. With a tapered nipple, its largest diameter is at its middleand is alsoat the plane of contact between the electrode sections. Thethreaded depth of the nipples is generally the same whether measured atthe ends of the nipple or at its center and this is true whether thenipple is straight or tapered. It is also usual, with either type ofconnecting nipple, that in the assembled joint each thread will possessa loaded flank, which is nearer the geometric center of the nipple, anda non-load bearing or idle flank which is opposite to the loaded flank.(That is, the idle flank is the flank nearer the ends of the nipple andthe loaded flank is the flank nearer the geometric center of the nipple,and this is how these flanks are defined in the present invention). Theloaded flank generally carries most, if not all, of the compressivestress between the nipple and the electrode sections; 1

In this type of joint, the half that is assembled first usually containslittle or no clearance at the idle flank while maximum clearance occursat the idle flank of the second half assembled.

Such electrode joints are generally mechanically weaker than thefull-bodied portions of the electrodes. To maintain the strength of thejoint as high as possible the nipple is normally produced from higherstrength graphite than the electrode itself. In processsing the nippleto higher strength the coefficient of thermal expansion (CTE) of theultimate graphite nipple is also normally increased as compared to'thegraphite of the electrode stock. This higher coefficient of thermalexpansion of the nipple relative to the electrode socket leads tothermal stresses within the joint during service on a furnace.Consequently the joints are particularly susceptible to breaking becauseof these thermal stresses which occur during heating and/or cooling ofthe electrodes. The high current loading of the electrode on modernelectric arc furnaces frequently causes additional joint stresses byoverheating of the nipple portion at the junction places between thenipbeen proposed by those skilled in the art to accomplish substantiallyeven distribution of thread clearance. For example, this problem andseveral proposed solutions for same are discussed in U. S. Pat. Nos.2,957,716; 2,970,854; 3,088,762; 3,134,616; 3,140,967; 3,517,954;3,517,957; and 3,550,270; and also in German Pat. Nos. 1,091,253 and1,100,838. The present invention also relatesto and is concerned with amore even distribution of clearance between the threads of the nippleand the electrode sockets and consequent reduction in thermal stressesbetween a nipple and the electrode sections into which it is threadedand offers a novel and advantageous approach for accomplishing this.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a nipple-electrode section pre-assembly in which there is a moreevenly distributed clearance (as compared to conventional commercialpractices) between the idle or non-load bearing flanks of the nipplethreads and the threads of the electrode section socket, so as toprovide room for thermal expansion of said threads and to therebyminimize the aforedescribed thermal stress conditions and to reduce theproblems created by these conditions.

It is another object of this invention to substantially evenlydistribute thread clearance throughout a nippleelectrode sectionpre-assembly, and also throughout an entire electrode joint assemblycomprising two electrode sections having threaded sockets in the endsthereof and a nipple threaded into said sockets, joining the electrodesections together. i

It is another object of this invention to accomplish the aforesaid moreeven distribution of thread clearance in an advantageous and practicalmanner which is also novel as compared to techniques which have beensuggested or taught by the prior art for solving this problem.

The invention comprises the making of an improved nipple-electrodesection pre-assembly, such as just discussed, for use in an electrodejoint comprised of said pre-assembly and a second electrode section,said nipple being threaded and said sections possessing correspondinglythreaded internal sockets extending in-' wardly from their end faces,by:

a. Providing at least one lengthwise hole between each end of thenipple, said lengthwise hole being substantially axial or parallel tothe axis and internally threaded for at least a portion of its length;

b. inserting a mechanical adjusting member, having external threadswhich correspond to the internal threads of the lengthwise hole, into athreaded end of the lengthwise hole, said member being capable of beingadjusted from the other end of the hole and to cause, or be capable ofcausing, relative axial movement between the nipple and the electrodesection of the pre-assembly;

c. threading the end of the threaded nipple containing the mechanicaladjusting member into the internally threaded socket of the pre-assemblyelectrode section to such a degree and in such a manner that byadjustment of the mechanical member it is possible to provide ormaintain a clearance between the non-load bearing flanks of the threadsof said nipple and of said threaded electrode socket, the other end ofsaid threaded nipple projecting outwardly form said socket; and

d. adjusting the mechanical member by inserting a suitable tool into thehole of the projecting end of the nipple and by turning the threadedmechanical member within the threaded lengthwise hole so as to bring orkeep the load bearing flanks of the nipple and the electrode socketsection into contact securing the nipple in this position, thusproviding said clearance between the non-load bearing flanks of thenipple threads and of said threaded electrode socket.

This pre-assembly is adapted to be added to a second electrode sectionto complete the making of the electrode joint by threading theprojecting end of the nipple into said second electrode section therebyalso providing substantially even distribution of clearance between thethreads of said nipple and the threads of the sockets of the electrodesections in the making of the final joint assembly.

As aforesaid, the mechanical member is adjusted by inserting a suitabletool into and/or down through the hole of the projecting end of thenipple, mechanically engaging the top of said member, and by turningsaid member within the hole. Typically the top of the mechanicaladjusting member will possess a slot or recess of suitable size andshape for engagement by means of a suitable tool such as a screwdriveror an Allen wrench of proper length. By turning the mechanically engagedtool or wrench at the projecting or exposed end of the nipple, theexternally threaded adjusting member is turned within the internallythreaded lengthwise hole in the nipple, causing the member to contactthe socket base and in turn cause or be capable of causing relativeaxial movement of the nipple with respect to the electrode section. Theturning of the adjusting member is continued until the load-bearingflanks of the nipple threads come or are caused to be kept in contactwith the adjacent or mating flanks of the threads of the electrodesocket thus securing the nipple in this position and thus also providingthe desired'clearance between the non-load bearing flanks of the threadsof said nipple and of said threaded electrode socket. The suitable toolemployed to turn the inner element is then, of course, removed from thelengthwise hole of the thus secured or fixedly pre-positioned nipple inthe electrode section. The pre-assembly is thus adapted to be added to asecond electrode section to complete the making of the electrode jointby threading the projecting end of the nipple into said second electrodesection and to thereby also provide substantially even distribution ofclearance between the threads of said nipple and the threads of thesockets of the electrode sections in the making of the final jointassembly.

The invention embraces not only the method of making the pre-assemblybut also the nipple-electrodesection pre-assembly itself, the method andconnection improvements involved, and an electrode joint assembly madeby coupling a second electrode section to the improved nipple-electrodesection pre-assembly.

Other objects, and coincident advantages, and a complete understandingof the invention will be apparcut to those skilled in the art after astudy of the drawings, and a reading of the specification and claims.

BRIEF DESCRIPTION OF THE DRAWINGS It has been found that the foregoingobjects are achieved by making the nipple-electrode section preassemblyillustrated in vertical cross-section in FIG. 3 and by using thispreassembly as a part of each joint assembly used in the electrodetrain. FIGS. 1 and 2 illustrate a pre-assembly of the same members asshown in FIG. 3 but with the members and thread flank arrangements ininitial stages or positions before the final desired positioning of themembers and thread clearance of FIG. 3 is obtained. FIGS. la, 2a and 3ashow expanded detail of the elliptical or encircled portions of thethreads and thread flanks of the nipple, electrodesection arrangementsof FIGS. 1, 2 and 3, respectively. FIG. 4 is an expandedcross-sectional'view of the lower circled portion of FIG. 3 andillustrates a typical threaded mechanical adjusting member and threadedlongitudinal hole which are used in carrying out the process of or inmaking the pre-assembly of the present invention. I

DETAILED DESCRIPTION OF THE DRAWINGS AND OF THE PREFERRED EMBODIMENTS InFIG. 1, the nipple 1, which as previously stated is preferably tapered,was threaded into a correspondingly threaded socket of electrode section2. Before this was done, the nipple was provided with a lengthwise axialhole 8 between its ends 6 and 9, which hole was internally threaded forat least a portion of its length and into which the threaded mechanicaladjusting member 5 was inserted. In the particular embodiment beingdescribed, the nipple had a major diameter of I0 54; inches, thediameter of the longitudinal hole was 1 14; inches and the diameter ofthe electrode section was 20 inches. The nipple also had a one-thirdpitch, i.e., three threads per inch, and a taper of 1 to 6, i.e., itsradius decreased by 1 inch for every 6 inches of length of the nippleaway from the maximum diameter. The end of the nipple containing themechanical adjusting member was threaded into the socket until its majordiameter, indicated generally at 3, coincided approximately with theplane of the face 4 of the electrode section and until it washand-tight, i.e., until the threads of both the nipple and electrodesocket section were fully or completely engaged, i.e., the threads werein contact on both flanks, as illustrated in FIG. la. In FIG. 2 thenipple was backed-off a calculated slight amount such as an eighth turn(i.e., 45), thus bringing about the loosely engaged thread flankrelationship illustrated in FIG. 2a; (It should be noted that in thesestages of making the pre-assembly the adjusting member 5 is positionedin such a manner in nipple hole 8 that it does not touch the bottom ofthe socket of the electrode section). This backing off of the nipplemakes it possible to pre-position" the nipple in the electrode sedtionsocket in the next step of the process and to thus provide the desiredclearance between the idle flanks of the threads of said threaded nippleand said threaded electrode socket, as illustrated and described in moredetail by reference to FIGS. 3, 3a and 4.

The backing-off of 45 of the nipple in the embodiment just described issatisfactory for a nipple having a pitch and taper as set forth. In amore general sense, the number of degrees backed-off will depend on thepitch and taper of the nipple because the clearance between the threadsis a function of these twovariables. For standard, nipples having aone-third pitch and a taper of l to 6, the number of degrees backed offwill typically be a value from about 45 to about 90; for standardnipples having a one-fourth pitch (4threads per inch) and a taper of lto 6, the number of degrees backed off will typically be a value fromabout 60 to about 135.

The mechanical adjusting member 5, shown in detail in FIG. 4, was thenadjusted with a suitable tool inserted down through the hole 8 to causethe bottom of said member to push against the base of the socket of theelectrode section 2, to thus cause relative axial movement between thenipple 1 and the electrode section 2 so as to provide the desired threadclearance or thread flank arrangement illustrated in FIG. 3a, and tocause a slightly increased gap or space between the base of the nippleand the electrode section socket bottom (illustrated exaggeratedly inFIGS. 3 and 4 as compared to H6. 1 and/or FIG. 2). This pre-positioningof the nipple caused the upper faces or load-bearing flank ll of thenipple (viz., the flank nearer the geometric center of the nipple) tocontact the mating faces of the threads of the socket and also caused orcreated a slight gap or clearance 12 at the idle or non-load bearingflank or side 13 of the thread, viz., the flank nearer the end 6 of thenipple.

As shown in FIG. 4, the mechanical adjusting member 5 is of properdiameter and external thread design so as to be capable of threadedengagement within the internally threaded lengthwise hole to therebyprovide for its axial adjustability within said hole and to thereby alsocause (and/or maintain) the aforesaid relative axial movement of thenipple with respect to the electrode section. It should be noted thatthe relative axial movement or positioning of the nipple with respect tothe electrode section may be caused in other ways than by use of member5 alone, such as by use of a ring l'as described in U. S. Pat. No.3,550,270, or a centering jig as described in U. S. Pat. No. 3,517,954.If such alternatives are used, then the mechanical adjusting member isemployed more to maintain and/or keep the desired thread clearancerather than to also establish or provide same.

The threading of the adjustable spacing means is preferably opposite tothe external threading of the nipple containing same. For example, thenipple normally possesses a right-hand thread and in such case theadjusting member and the hole in the nipple are preferably provided withmatching left-handed threads so as to resist further turning of theadjusting member after completion of the pre-assembly and when threadinga second electrode section onto the other projecting end of the nipple.Adjusting member 5 possesses a keying means 7, such as a slot or acornered recess therein, so that it may be turned by means of a suitabletool, such as a screwdriver or Allen wrench, inserted down or throughhole 8 and turned therein. Regardless of whether it is employed alone orwith an alternative such as the aforediscussed ring or centering jig, inthe final positioning of the nipple in the pre-assembly, member Sisalways adjusted within hole 8 until the nipple is fixed or securedfirmly in place in the electrode section socket, with the load bearingthread flanks in contact, and with clearance between the non-loadbearing flanks as shown in FIG. 3a.

Mechanical member 5 may be provided with a flange 5a at its base so asto provide more balanced lifting or sustaining of the nipple in itsraised position illustrated in FIG. 3a. It should also be appreciatedthat more than one hole 8 and mechanical adjusting member 5 may beemployed in carrying out the invention, although this is not generallynecessary or desirable. Any such hole or holes used should besubstantially axial and/or parallel to the nipple axis so as to assureeven balancing of the nipple in the socket of the pre-assembly electrodesection and thus guard against cocking of the nipple therein.

As shown in FIG. 4, the hole 8 is internally threaded for only a portionof its length and at one end thereof. The hole, of course, may bethreaded in several ways. For example, it may be threaded its entirelength so as to facilitate the insertion of the mechanical adjustingmember 5 from either end of the nipple; or the hole 8 may be unthreadedfor a short distance from the end of the nipple and of larger diameterthan the threaded portion, so as to facilitate easy entry and threadedengagement of the adjusting member therein.

When an electrode-nipple pre-assembly as described herein is added to asecond electrode section of an electric furnace column or train, thenipple in the resulting 3-membered joint (viz. two electrode sectionswith the nipple half-threaded into each) will be so located that therewill be a substantially even distribution of clearance between the idleflanks of the threads of both halves of the nipple in the electrodesection sockets of the final joint asembly, rather than the common andobjectionable condition typically encountered in the prior art of noclearance at the idle flank of the threads of the nipple-half assembledfirst and maximum clearance at the idle flank of the threads of thesecond nipple-half assembled. Consequently there is a reduction in thethermal stresses between the nipple and the electrode sections intowhich it is threaded with the result that there is a reduction in thedegree of splitting and breakage of the joint in furnace operation.

The net effect, therefore, of centering or balancing the nipple in thejoint, is that there are fewer mechanical breakdowns or failures in theoperation of the furnace. There are also other advantages inherent inmaking the nipple-electrode section assemblies and joints in accordancewith the present invention. For example, the incidence ofthread-stripping from the sockets of the threaded electrode sections isvirtually precluded because of the more uniform thread loading attendingthe centering of the nipple.

It is to be understood that the invention is not limited to the specificdetails which have been offered merely for illustrative purposes andthat modifications may be made within the scope of the appended claimswithout departing from the spirit of the invention.

I claim:

1. An electrode section nipple assembly comprising:

a. A cylindrical electrode section containing internally threadedsockets extending into the section from each of its end faces;

b. a threaded nipple, having at least one lengthwise hole therein whichis substantially axial or parallel to the axis of the nipple, threadedinto and positioned in one of the sockets of said electrode section withthe load bearing flanks of the nipple threads, which are the flanksnearer to the geometric center than to the ends of the nipple in contactwith the mating faces of the threads of the electrode section socket andwith a space between the base of the nipple and the bottom of theelectrode section socket; and

c. a mechanically adjustable spacing member situated within thelengthwise hole of the nipple and the space between the base of thenipple and the bottom of the socket of the electrode section which isadjustable through the opposite end of the hole in the nipple to holdthe load bearing flanks of the nipple threads and the electrode socketsection threads in contact thereby securing the nipple in this positionin the electrode section socket, and

claim 1 wherein the threading of the adjustable spacing member isopposite to the external threading of the nip ple containing same.

3. In an electrode joint comprising two electrode sections containinginternally threaded sockets which extend inwardly from end faces of saidsections and a threaded nipple connecting said sections by beingthreaded into said sockets, the improvement wherein the joint includesthe assembly of claim 1.

1. An electrode section nipple assembly comprising: a. A cylindricalelectrode section containing internally threaded sockets extending intothe section from each of its end faces; b. a threaded nipple, having atleast one lengthwise hole therein which is substantially axial orparallel to the axis of the nipple, threaded into and positioned in oneof the sockets of said electrode section with the load bearing flanks ofthe nipple threads, which are the flanks nearer to the geometric centerthan to the ends of the nipple in contact with the mating faces of thethreads of the electrode section socket and with a space between thebase of the nipple and the bottom of the electrode section socket; andc. a mechanically adjustable spacing member situated within thelengthwise hole of the nipple and the space between the base of thenipple and the bottom of the socket of the electrode section which isadjustable through the opposite end of the hole in the nipple to holdthe load bearing flanks of the nipple threads and the electrode socketsection threads in contact thereby securing the nipple in this positionin the electrode section socket, and thus also providing a clEarancebetween the non-load bearing flanks of the nipple threads and saidthreaded electrode socket; said lengthwise hole being internallythreaded for at least a portion of its length and said spacing memberbeing correspondingly externally threaded thereby providing for itsadjustability within said hole.
 2. An electrode section nipple assemblyaccording to claim 1 wherein the threading of the adjustable spacingmember is opposite to the external threading of the nipple containingsame.
 3. In an electrode joint comprising two electrode sectionscontaining internally threaded sockets which extend inwardly from endfaces of said sections and a threaded nipple connecting said sections bybeing threaded into said sockets, the improvement wherein the jointincludes the assembly of claim 1.